Sound reproducing apparatus



July 9, 1940. B. CORNWELL 2,297,240

I SOUND REPRODUCING APPARATUS Filed Feb. 12, 1938 H! In, 7

a 6000000OOOO 00000000000 VOQOOOOOO l N V E NVTO R Zl'wwl 31,766 am Well ATTORN EYS Patented July 9, 1940 UNITED STATES PATENT OFFICE SOUND REPRODUCENG APPARATUS Application February 12, 1938, Serial No. 190,161

3 Claims.

This invention relates to sound reproduction apparatus and particularly to a voice coil support and its mounting on diaphragm or other vibrating element of a loud speaker or the like.

An object of the invention is to provide a voice coil mounting construction which will facilitate the use of relatively stiff material, permitting the necessary circumferential flexibility while retaining longitudinal stiffness and lightness.

A further object is to improve the bond between the support, the voice coil and the diaphragm respectively, providing a strong permanent connection. In a preferred form the diaphragm mounting is arranged to reduce objectionable stresses and to improve transmission of vibrations from the voice coil support to the diaphragm.

Other objects, including the provision of a mounting that inexpensive, readily constructed and assembled and permanent, together with specific features of construction and arrangement, will appear from the following description considered in connection with the accompanying drawing in which,

Fig. 1 is a perspective view of a vibratory element in the form of a double cone diaphragm with the voice coil and voice coil support mounted thereon;

Fig. 2 is a median vertical section of the lower part of the structure shown in Fig. 1 on an enlarged scale;

Fig. 3 is a similar section on still further enlarged scale showing one form of voice coil, support and diaphragm mounting;

Fig. 4 is a fragmentary view similar to Fig. 3 showing another form of mounting;

Fig. 5 is a side elevation of one form of voice coil support; and

Figs. 6 and 7 are similar views of modifications of the support.

In the specific embodiment shown the voice coil support S is cylindrical and is formed of suitable thin and very rigid material such as mica or a metal foil of duralumin, phosphor bronze or the like. It is mounted on the diaphragm or cone C at the apex A between the outer conical portion it and the inner cone or plunger H. The diaphragm C is preferably formed of continuous deposit of fibrous material suitably varied in deposition and stiffening to impart the desired vibratory characteristics.

C-ne form of mounting of support S is shown in 1-3, in which the cone apex A is formed with a reentrant groove G into which the upper margin of the voice coil support S is fitted and held by suitable means such as cement l3.

Support S may be provided with perforations I l positioned for penetration by the cement in groove G, and preferably located so that the cement will pass through perforations hi and lock the upper end of support S to the diaphragm C.

Groove G may be contoured in various ways in accordance with the particular structure and operating conditions of the diaphragm C and other parts of the loud speaker with which such diaphragm is associated. An advantageous arrangement is illustrated in Fig. 4, in which the groove G is formed with little, if any, angle between the cone C and the adjacent portion of the groove G, the other side of groove G extending downwardly and adjacent the support S, the groove being arranged so that the cement 53 may attach the diaphragm to both sides of the support S and preferably extend through theapertures M.

This arrangement is particularly advantageous because the axial vibrations of the voice coil support S, which with high powered loud speakers may involve very heavy impulses, are transmitted to the main body I!) of the cone at an obtuse angle and particularly without any reentrant cone angle, tending to avoid lateral pressure on the support S, and consequent transverse strain on the extremely thin material of which the support is made.

The voice coil support S may be provided with perforations throughout its area for the purpose of increasing its lightness and improving its efficiency. Since the main stresses on this support are in an axial direction, the perforations M are preferably arranged to provide unbroken longitudinal areas of the support between a series of such perforations, the perforations serving to facilitate the formation and maintenance of the support in a true cylinder even when constructed of exceptionally stiff material. The perforations it may be arranged in the cementing zone as indicated in Fig. 5, may be in suitably staggered series of holes l5 as shown in Fig. 6, or may take the form of fine longitudinal slits It arranged in longitudinal series, as shown in Fig. 7.

The voice coil V is mounted on the lower end of support S in known manner and is cemented in place. The support S may advantageously be perforated adjacent coil V to permit the cement it to pass into the apertures l1, and, if desired, through and around such apertures in order to afford an extremely strong bond at this point. This arrangement enhances the stiffness of the support S which in fact may be of substantially greater strength and stiffness than the original unperforated material of the support.

Where the support S is constructed of mica the perforations are particularly valuable in assisting the formation and maintenance of a true cylindrical shape, which tends to be obstructed by the laminated arrangement of the mica.

I claim:

1. In a sound reproducing apparatus, a generally conical diaphragm having an annular groove formation for the reception of an end of the voice coil support, a cylindrical voice coil support having one end positioned in said groove formation with the inner and outer cylindrical surfaces of said support disengaged from the walls of said groove formation, and a mass of adhesive in said groove formation in extended contact with the walls thereof acting to secure the end of said support to said diaphragm, a portion of said adhesive mass being positioned around the outside of said support, another portion of said adhesive mass being positioned around the inside of said support, a row of apertures being provided around the end of said support within said groove formation but spaced from said end to leave a continuous marginal strip at said end, and continuous intermediate portions of said adhesive mass extending through said apertures and joining the inside and outside portions of said adhesive mass, whereby a firm light-weight attachment is provided having the strength and lightness for transmission of both small and large voice coil movements in each axial direction occurring during sound reproduction.

2. The construction as set forth in claim 1 in which said groove formation is a V-shaped groove between an outer portion and a reentrant inner portion of said diaphragm.

3. The construction as set forth in claim 1 in which said groove formation has a nearly axial Wall and a generally radial shoulder between an outer portion and a reentrant inner portion of said diaphragm.

LIONEL BRICE CORNWELL. 

